oops... missed some docs from main

Author: lyc8503

Doc/library/http.server.rst

@@ -253,7 +253,12 @@ instantiation, of which this module provides three different variants:
       readable description of the error.  The *explain* argument can be used to
       provide more detailed information about the error; it will be formatted
       using the :attr:`error_message_format` attribute and emitted, after
-      a complete set of headers, as the response body.
+      a complete set of headers, as the response body.  The :attr:`responses`
+      attribute holds the default values for *message* and *explain* that
+      will be used if no value is provided; for unknown codes the default value
+      for both is the string ``???``. The body will be empty if the method is
+      HEAD or the response code is one of the following: :samp:`1{xx}`,
+      ``204 No Content``, ``205 Reset Content``, ``304 Not Modified``.
 
       The *extra_headers* argument can be a key-value tuple list which
       specifies additional headers to be sent in the response (for